Explore the fundamentals of electricity, including circuits, current, voltage, and resistance, to understand how electrical devices operate.
Electricity – Formula & Equation Sheet
Essential formulas and equations from Science, tailored for Class X in Science.
This one-pager compiles key formulas and equations from the Electricity chapter of Science. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
I = Q/t
I represents current (amperes), Q is charge (coulombs), and t is time (seconds). This formula calculates the current as the rate of flow of charge. Tip: 1 A = 1 C/s.
V = W/Q
V is potential difference (volts), W is work done (joules), and Q is charge (coulombs). It defines potential difference as work done per unit charge. Example: Moving 2 C with 24 J work gives V = 12 V.
R = ρl/A
R is resistance (ohms), ρ is resistivity (Ωm), l is length (m), and A is cross-sectional area (m²). This shows resistance depends on material and dimensions. Tip: Longer or thinner wires have higher resistance.
P = VI
P is power (watts), V is potential difference (volts), and I is current (amperes). It calculates the power consumed by a device. Example: A bulb at 220 V and 0.5 A uses 110 W.
H = I²Rt
H is heat (joules), I is current (amperes), R is resistance (ohms), and t is time (seconds). Joule's law of heating. Tip: Heat increases with the square of current.
1/Rp = 1/R₁ + 1/R₂ + ...
Rp is equivalent resistance (ohms) of parallel resistors R₁, R₂, etc. The total resistance decreases in parallel. Example: Two 10 Ω resistors in parallel give 5 Ω.
Rs = R₁ + R₂ + ...
Rs is equivalent resistance (ohms) of series resistors R₁, R₂, etc. The total resistance adds up in series. Example: Two 10 Ω resistors in series give 20 Ω.
V = IR
V is potential difference (volts), I is current (amperes), and R is resistance (ohms). Ohm's law, fundamental for circuit analysis. Tip: Directly proportional relationship.
E = VIt
E is energy (joules), V is potential difference (volts), I is current (amperes), and t is time (seconds). Calculates energy consumed by a device. Example: 220 V, 0.5 A for 1 hour is 396 kJ.
P = I²R
P is power (watts), I is current (amperes), and R is resistance (ohms). Alternative power formula, useful when voltage is not known. Derived from P = VI and V = IR.
Equations
Ohm’s Law: V = IR
Defines the relationship between voltage, current, and resistance in a conductor. Essential for solving circuit problems. Real-world use: Designing electrical circuits.
Series Resistance: Rs = R₁ + R₂ + R₃ + ...
Total resistance in a series circuit is the sum of individual resistances. Tip: Current remains the same across each resistor.
Parallel Resistance: 1/Rp = 1/R₁ + 1/R₂ + 1/R₃ + ...
Reciprocal of total resistance in parallel is the sum of reciprocals of individual resistances. Tip: Voltage remains the same across each resistor.
Power: P = V²/R
Calculates power using voltage and resistance. Derived from P = VI and Ohm's law. Useful when current is not directly known.
Current: I = V/R
Calculates current using voltage and resistance. Direct application of Ohm's law. Example: 12 V across 4 Ω gives 3 A.
Energy: E = P × t
Energy consumed is power multiplied by time. Real-world use: Calculating electricity bills. Example: 100 W for 10 hours is 1 kWh.
Resistivity: ρ = RA/l
Relates resistance to material properties and dimensions. Tip: Resistivity is a material property, independent of shape.
Charge: Q = It
Charge is current multiplied by time. Useful for calculating total charge flow. Example: 2 A for 5 seconds is 10 C.
Work: W = VQ
Work done to move charge across a potential difference. Example: Moving 2 C across 12 V requires 24 J.
Heat: H = VIt
Heat produced in a resistor is voltage times current times time. Alternative to H = I²Rt, emphasizing voltage's role.
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